Bill is correct in his location description. My 2003 S40 tranny dip stick is located where he describes. My dipstick looks like a round yellow plunger. This is on the base 1.9L 4cyl turbo engine. I would think yours would be similarily located.

I would say look again. Maybe you are seeing it, but not seeing it. : )

Rich
Apex, NC

S40 S40
https://startpage.com/do/search
http://www.volvocars.com/us/own/owner-info/owners-manuals
http://new.volvocars.com/ownersdocs/2000/2000_SV40/00sv40_00.htm

Pg 109 engine compartment
item 7 oil dipstick for tranny
Volvo goofed and didn't point to it's location

The tranny is to the drivers side of the engine block
look directly left of the battery, down low, buried amidst a large
hose It's a yellow plastic end. (It's hard to see)

It should be left of the battery and in line with the brake master cylinder

Once you find it, there's two marks, hot and cold.
Check it after it's warmed up is best, keep the engine running while you check
it. You are interested in the level being correct and also in the condition
of the tranny fluid. It need's periodic flushing. There's writeups and videos
explaining how you can do it. Avoid the power flushes at garages.
Healthy ATF should be red and not brown.

Bill